Current electronic devices are designed to become more and more user-friendly. Furthermore, in order to cope with different circumstances, transportability and flexibility are elements inevitable for the design of such electronic devices.
Usually, a display contains numerous functions, such as a light guiding plate and a diffusion plate. For instance, a light guiding plate has a microstructure protruding from its surface for uniform light guide. Commonly, the microstructure in the optical plate is manufactured by lithography. Taiwan Patent No. I294430 discloses a method for manufacturing such an optical plate, and the method is described below. Firstly, a resist layer is coated on a surface of a substrate. Light is irradiated through a mask to expose the resist layer, and the exposed resist layer is then developed and baked to form a microstructure thereon. After coating a conducting layer on the resist layer, a core insert having a microstructure is electroformed on the conducting layer. Finally, the core insert is used to form the optical plate by injection molding. Since the foregoing lithography patterning includes steps of coating, soft baking, exposing, post baking, developing and hard baking, etc., the method is complicated.
Such an optical plate may be manufactured by another method to define its microstructure. In this method, a laser beam is irradiated onto a core insert to form a cavity thereon, and the core insert is then used to form the optical plate by casting or injection molding. Taking a carbon dioxide laser beam as an example, the carbon dioxide laser beam heats up a workpiece surface according to photothermal effect, and the heat is then conducted into the workpiece. When the heat energy is large enough, a part of the workpiece may be melted or vaporized. Then, the carbon dioxide laser beam scans the workpiece for photolithography or cutting the workpiece. As the carbon dioxide laser beam has a wavelength of approximately 10.6 μm, it's suitable for working on a brittle material, e.g. glass, polymer or oxide.
The carbon dioxide laser beam reaches the foregoing objective such as photolithography or cutting through photothermal effect. Owing to photothermal effect, the heat conducted internally in the workpiece causes the so called heat-affected zone in the workpiece, which leads to defects thereon, e.g. bulges, scorch, resolidification and splashes formation. On the other hand, when the optical plate is employed as a light guiding plate, its microstructure has a size of approximately 100 μm, and it's well known that the resolution of the optical plate can be improved by decreasing the size of the microstructure. However, a microstructure defined by the carbon dioxide laser beam has a size in a range from 200 to 300 μm. Therefore, the carbon dioxide laser beam cannot be used to define a microstructure having a size less than 100 μm. In sum, the carbon dioxide laser beam has disadvantages that the microstructure so made is oversized and thus the optical plate is defected. As such, the carbon dioxide laser beam is disadvantageous in manufacturing an optical plate having a microstructure, such as a light guiding plate.